1. Field of the Invention
This invention relates to a method of and an apparatus for producing or making a diamond whose properties, such as for example hardness, heat conductivity, and electrical insulation, are superior to other materials. More particularly, the invention relates to a method of and an apparatus for inexpensively and quickly producing or making the diamond whose properties are the same or superior to natural diamond and which does not contain any impurities.
Artificial diamond making methods are basically classified into two categories: one is an extra-high pressure high temperature method and the other includes low pressure CVD methods.
The former method involves reaction and synthesization in a container under tens of thousands of atmospheric pressure and at several thousands of temperatures. An apparatus thereof is thus extremely expensive.
The latter, low pressure CVD methods, includes a DC plasma method, a heat filament method, a microwave CVD method, a spattering method and an ionized deposition method, and an apparatus thereof is generally far less expensive than compared with an apparatus for the extra-high pressure high temperature method.
Any of the low pressure CVD methods, excluding the DC plasma method, are inferior to the extra-high pressure high temperature method in that they are relatively slow in their production speed, for example, at most several +10 .mu.m per hour in generating speed of diamond films. On the other hand, the DC plasma method, using a rather inexpensive apparatus, allows high speed production of 180 to 250 .mu.m per hour.
Several methods of diamond production by such a DC plasma method have been found. One is a DC arc plasma method and the other is a DC plasma jet method. The former is constructed as shown in FIG. 18 in which an arc 3 is generated between an anode 1 and a cathode 2, and a mixture of hydrogen gas 13 and methane gas serving as a raw material gas 12 flows to a direction intersecting with the arc 3. On the downstream side of a supply opening of a raw material gas feed tube 9 and under the arc 3 is arranged a substrate 5 where the diamond is produced on the surface thereof.
In FIG. 18, numeral 4 indicates a plasma flame, 6 a cooling water inflow tube, 7 a cooling water spill tube, 8 a DC power supply and 11 a gas outlet of a container 10, respectively.
The latter, the DC plasma jet method, is constructed as shown in FIG. 19, wherein a cylindrical anode 1 is disposed around a cylindrical cathode 2, and a mixture of hydrogen gas 13 and methane gas 12 serving as a raw material gas 12, and plasma gas 14 flow through a cylindrical passageway 16.
In FIG. 19, numeral 22 indicates an insulating material.
The above two methods, compared with other CVD methods, are remarkably quick in production speed, 180 to 250 .mu.m per hour, which is equal to the extra-high pressure high temperature method.
In these methods, a plasma generating apparatus, a substrate supporting device, a substrate cooling apparatus and the like are incorporated in an atmosphere regulative container, where diamond is produced by hydrogen and methane gases with an arc 3.
Such methods have the following disadvantages:
1. In the DC arc discharge method, the flow of a mixture gas perpendicular to the arc does not allow a sufficient time for reaction.
2. In the DC plasma jet method, because of the fact that a gas for generating a plasma is a mixture gas for producing diamond, precipitation of the partial carbon in the plasma generating apparatus is responsible for electric short circuiting between the anode 1 and the cathode 2, and thus it is difficult to generate a stable arc.
3. Further, owing to the same reason as above, i.e. the electric short circuiting between the two electrodes in a short time, the raw material gas cannot increase in its density.
The synthesizing speed in these methods is not capable of exceeding 250 .mu.m per hour. Further, a sufficient amount of active hydrogen atom generated in the plasma flame is required for increasing the purity of the diamond produced on the substrate. In either of the DC plasma methods, however, the reaction of hydrogen does not progress, which results in insufficient generation of active hydrogen. Consequently, the diamond is not rapidly produced on the substrate. As an impurity which determines the properties of the diamond, carbon left behind in the process of producing the diamond is precipitated as amorphous carbon or graphite-like carbon.